hi everyone and welcome to this video just a recap of what chapters we have covered this semester we have covered respiration and photosynthesis and now we'll be moving on to a different kind of a2 chapter so these two are very related to each other my next two will be related to each will be different but related to each other as well the next two will be on homeostasis hormones and basically the nervous system so chapter 14 is homeostasis we'll be learning thermal regulation also regulation control of blood glucose concentration number four plant hormones so these are all the ways um the human body regulates and number four is about plants now for control and coordination which is chapter 15 there's also four parts so how the nervous system works how the muscles work and how the menstrual cycle works the fourth part again is about plants so this is what we're going to do we are going to be talking about chapter 14 first three parts then chapter 15 three parts then we'll talk about plant hormones all together okay so that's the plan without further ado let's talk about chapter 14 homeostasis now again homeostasis has four parts and this is part one thermal regulation so what about thermoregulation now before we talk about any regulation actually we need to talk about what in the world is homeostasis in the first place and define a few terms after we define them then it's going to be easier to talk about things in the right terminology so homeostasis is the maintenance of a constant internal environment so you want to make sure that your internal environment aka your body fluids have a constant optimal temperature ph glucose concentration etc this requires the set point to be kept stable within narrow limits in the body what do we mean by set point so set point could be an optimum temperature or optimum ph at different parts of the body optimum water potential in the blood fluid so that's a set point for example 37 degrees is the set point the furthest week we'll go is probably 38 39 degrees which you have a fever already your body will try to keep it around 37 okay because on the low side will be 36 right generally it's only a few degree difference from 37 so that's a narrow limit that's what this means and this is irrespective of changes in the external environment so internal environment temperature might be different from the external environment temperature so again factors such as temperature water potential and glucose concentration must be maintained through homeostasis why because it will affect cell function the idea is to have the internal environment that is stable and internal environment that functions optimally how is this control systems working is probably working using the negative feedback mechanism now what is the negative feedback mechanism here are a few key words you need to know you need a stimulus something to start it off you need a receptor a control center or coordinating center same thing effector and a response and a response that counteracts okay or is opposite to the stimulus in order to restore the norm or set point let's look at each component and break it down one by one okay it's very important this negative feedback mechanism you will see all these words again and again throughout this chapter so what is stimulus stimulus uh defined is defined as the internal or external change in a factor away from the norm or set point so a decrease in body temperature increase in body temperature but how does your body know it needs cells a tissue and organ receptors which detect the stimulus then this stimulus this information gets sent to this message gets sent to the coordinating center and the coordinating center receives this message from the receptor and determines the appropriate response these messages can come in the form of hormones and nerve impulses so it could be a chemical molecule or it could it could be a nervous response through your nerves and stuff okay only the stimulus reaches systems threshold or is strong enough then the coordinating center would send the message to infected so your body isn't sensitive towards every single stimuli it's sensitive towards most now the effector which gets the message from the coordinating center can then carry out a corrective reaction in order to correct the external or internal change the response is the reaction carried out by the effector so effector is such it's like a tissue organ the response is what they do and in negative feedback the response will definitely counteract the stimulus so you can see here is blue the body works and counteracts it moving it away from that change and returning it back to the set point or norm so if the stimulus is that there is a decrease in body temperature the response that counteracts that stimulus would be to increase the body temperature if the stimulus is a increase in body temperature the response will be the opposite of that it will be to um it will be to decrease the body temperature now it's easy to see this negative feedback mechanism as something that happens once in a while but actually it is continuously happening negative feedback is a continuous monitoring of the factor affecting the internal environment this results in many corrective actions so you will get this kind of graph if you measure say body temperature throughout the day the factor will fluctuate around the norm or set point or in this case the body temperature will fluctuate around the norm or set point which is around 37 degrees why is that that's probably due to a stimulus from outside or inside yeah and then a response that counteracts that stimulus but then results in a lower level with this result might result this response might result in a new disturbance or new stimulus and um since now it's too low the negative feedback response okay negative feedback mechanism is used again to push the temperature up back to the optimum set point so throughout the day the body temperature will tend to fluctuate up and down like this but always around the normal set point now negative feedback again is is when the response counter existing lie but positive feedback is the opposite of that positive feedback is a thing it is not used to maintain homeostasis is used in other things so positive feedback is when the response re-enforce the original statement so if the stimulus is high then the response will make it even higher or even more intense whereas in negative feedback as we said response counteracts the original seamless positive feedback is more uncommon but it's it does exist okay and negative feedback is common to maintain homeostasis mainly now an example of positive feedback which is very famous is labor pains so with uh pregnant when pregnant women are given birth the labor pains get more and more intense the body doesn't regulate that and make it averagely quite painful now it's going to get more and more painful each time it doesn't fluctuate ripening fruit of fruit as well the fruits get riper and ripple over time they don't suddenly become unripe now surprisingly inhalation of co2 happens that way the more co2 you inhale the more you rise you need more oxygen so the more you inhale but if there's only co2 around then you inhale even more co2 so it's a positive feedback you eventually run off breath okay it will reach a point where it cannot progress anymore and explodes okay a system just doesn't work anymore whereas for negative feedback it's very useful to maintain homeostasis okay because the response counter is original stimulus right so this is very useful in examples like maintaining blood glucose levels temperature oxygen abc so we um expect in positive feedback that the graph would go right straight up like this exponentially whereas the negative feedback you will fluctuate up and down now positive feedback doesn't come out very often but you should know it just for general knowledge